Cathedral, Forge, and Waterwheel Part 4

Metallurgy: The Waterpowered Blast Furnace If the cathedral was the aesthetic marvel of the Middle Ages, a less prepossessing structure was, in the opinion of R. J. Forbes, "the greatest technical achievement" of the period.97 In the medieval invention of the blast furnace, the waterwheel once more played a central role. In the medieval invention of the blast furnace, the waterwheel once more played a central role.

The spread of waterpower from tributaries and small rivers to the larger rivers was made possible by the construction of dams and millraces, and was signaled in the doc.u.mentary record by the marked increase after 1300 in laws and lawsuits involving navigation rights versus power rights.98 The vertical waterwheel acquired new accessories, such as the mechanical governor that helped grind the grain and sift the flour at Clairvaux and elsewhere: a square segment of the millstone axle acted as a cam, catching against a projection on the hopper, causing it to shake and discharge its flour. The faster the waterwheel turned, the faster the hopper shook. The vertical waterwheel acquired new accessories, such as the mechanical governor that helped grind the grain and sift the flour at Clairvaux and elsewhere: a square segment of the millstone axle acted as a cam, catching against a projection on the hopper, causing it to shake and discharge its flour. The faster the waterwheel turned, the faster the hopper shook.99 A number of new applications of waterpower appeared, including the important metallurgical function of wire drawing and the important mining function of water pumping, but the most momentous came in smelting iron ore in the new blast furnace. Time and place of origin of the furnace are obscure. The Chinese waterpowered blast furnace evidently migrated as far west as Persia, but how early is unknown, and further transmission is undoc.u.mented. The earliest known blast furnace in Europe has been excavated at Lapphytten, Sweden, and is believed to have operated before 1350.100 The old process of reducing iron ore to a spongy bloom and hammering it into wrought iron had been an obvious candidate for mechanization via the waterwheel and trip-hammer, a combination in wide use by the fourteenth century. The waterwheel was now enlisted to pump pairs of bellows several feet in diameter, mounted in tandem and blowing alternately through a common tuyere, increasing the draft and decisively raising the temperature in the furnace. The draft was also increased by the furnace's new form. What had once been little more than a pit and a stubby chimney had gradually risen into a novel shape: a tall masonry structure square in plan, mounted over a crucible (firebox) built on a flat stone hearth. The chimney was made up of two vertical pieces, a short lower one shaped like an inverted truncated pyramid (resembling a grain mill hopper in profile), topped by a tall right-side-up truncated pyramid.101 The whole structure rose eighteen or twenty feet above ground, though the hearth within was no more than a foot square. By 1400 blast furnaces were operating (in addition to Sweden) in Styria (Austria), the Rhine valley, and the neighborhood of Liege (Belgium). The whole structure rose eighteen or twenty feet above ground, though the hearth within was no more than a foot square. By 1400 blast furnaces were operating (in addition to Sweden) in Styria (Austria), the Rhine valley, and the neighborhood of Liege (Belgium).102 The stronger blast of air in the new furnaces heated the ore to a point where carbon uptake became very rapid, producing an alloy of about 4 percent carbon and 96 percent iron. This metal had a much lower melting point than pure iron (about 1,100 C as against about 1,530 C), making possible the casting of molten iron. Almost at a stroke the blast furnace carried the ancient handicraft of iron making into the industrial age. Cast iron became the sought-after intermediate product of an entirely new two-stage process.

A waterpowered blast furnace could run continuously, for weeks or months at a time. The sand and clay containing the iron ore were mixed with a limestone flux to form the furnace's charge, which was layered alternately with charcoal. As the ma.s.s heated, the sand, clay, and limestone formed a slag that floated on top of the heavier molten iron. The slag was removed periodically from an opening near the top of the furnace, the iron run off through another at the bottom.103 In early blast furnaces, the iron ran into a bed of sand to cool in successive batches, but the quant.i.ties that could be produced brought about an expansion of the sand bed into a system given a picturesque medieval nomenclature. Starting in a ca.n.a.l called the "runner," the molten metal flowed into several large, shallow depressions. The image of the depressions reminded smiths of a sow with suckling pigs, and the term "pig iron" was born. In early blast furnaces, the iron ran into a bed of sand to cool in successive batches, but the quant.i.ties that could be produced brought about an expansion of the sand bed into a system given a picturesque medieval nomenclature. Starting in a ca.n.a.l called the "runner," the molten metal flowed into several large, shallow depressions. The image of the depressions reminded smiths of a sow with suckling pigs, and the term "pig iron" was born.

The cooled pig, weighing a couple of hundred pounds, was transported to a secondary furnace called a "finery," a charcoal-fired hearth equipped with two air blasts, one to supply draft for the fire and another to play on the iron as it heated, its oxygen combining with the carbon in the metal and blowing off in smoke, leaving pure (wrought) iron. These air blasts were also soon powered by waterwheel and continued to be on into the nineteenth century, when no one could remember why the iron chunks were called pigs.104 The new system produced much more iron with much less labor, reducing cost and multiplying applications. It did not bring an immediate s.h.i.+ft to the casting of iron implements. The smith continued to work at his forge, with either pig or bloomery iron, first shearing a piece of roughly the proper size with chisel and hammer, then reheating and hammering into shape as blade for sickle, scythe, ax, adze, or mattock, as fire tong, hinge, tip for spade, wool comb, axle part, or the universal cauldron, used for cooking, brewing, and bathing the baby.105 A product of the smith: the universal cauldron, used for cooking, brewing, and bathing the baby. [British Library, Ms. Cotton Claudius B IV, f. 28.)]

The fourteenth-century smith still commanded respect, but he had become less of a mysterious specialist in aristocratic arms and armor and more of a homely and familiar figure in the community, valued as a craftsman, but not always welcome as a neighbor. A contemporary poem ent.i.tled "A Complaint Against the Blacksmiths" gives a picture of the forge in the alliterative style of Piers Plowman: Piers Plowman: The crooked codgers cry after: Coal! Coal!And blow their bellows till their brains are all bursting.Huff! Puff! says the one, Haff! Paff! says the other.They spit and they sprawl and they tell many tales.They gnaw and they gnash and they groan all togetherAnd hold themselves hot with their hard hammers.Of a bull's hide are built their bellies' ap.r.o.ns,Their shanks are sheathed against flickering flames.Heavy hammers they have that are hard to handle.Stark strokes they strike on a stock of steel.106 In 1397 in London, smiths were being invited to leave neighborhoods because of "the great nuisance, noise, and alarm experienced in divers ways by neighbors around their dwellings." A spin-off branch of the trade was found even more objectionable. The spurriers (spur makers) were reputed to "wander about all day without working," getting drunk and "blow[ing] up their fires so vigorously" at night that they blazed, "to the great peril of themselves and the whole neighborhood." In 1377 the neighbors of a London armorer named Stephen atte Fryth lodged a formal complaint against him, alleging that "the blows of the sledge-hammer when the great pieces of iron...are being wrought into...armor, shake the stone and earthen party walls of the plaintiffs' house so that they are in danger of collapsing, and disturb the rest of the plaintiffs and their servants, day and night, and spoil the wine and ale in their cellar, and the stench of the smoke from the sea-coal used in the forge penetrates their hall and chambers."107 "The Most Pernicious Arts": Firearms from China The blast furnace arrived in the West just as a new use for metal appeared, quite suddenly but with little fanfare: firearms. In China, gunpowder weapons had matured over some four centuries, from alchemists' experiments with explosive mixtures to primitive guns embodying three basic features: a metal barrel, a dependable explosive, and a projectile efficiently fitted to the bore.

While the firearms evolution proceeded in China, Europe continued to tinker with the crossbow. The English longbow, actually Welsh in origin, played so conspicuous a role in the English victories of Crecy (1346) and Poitiers (1356) that debate over the rival merits of the two bows has continued into the twentieth century. Despite the longbow's more rapid rate of fire, the decisive evidence in favor of the crossbow seems to be the failure of the longbow to diffuse on the Continent and the fact that, despite Crecy, Poitiers, and Agincourt (1415), the French won the Hundred Years War. In any case, it was the crossbow that was susceptible of technical improvement, which it received in two directions. The old wood, bone, and composition materials were replaced, from about 1370, by steel. The resulting bow had an extreme range of 400 to 450 yards and required a more powerful c.o.c.king mechanism, three different forms of which were invented. The "goat's foot" was a long lever atop the stock, the cranequin a ratchet device moved by a horizontal crank, and the windla.s.s a winch powered by a small double crank.108 More effective bows and greater availability of iron brought on a defensive reaction: a steady increase in the use of plate armor. The mature coat of mail, or hauberk, fas.h.i.+oned of interlinked iron rings, remained through the first half of the fourteenth century the fundamental protection of the torso, with plates added to cover arms and legs. The articulation needed to permit freedom of movement was achieved mainly through "lames," overlapping leaves pinned by rivets fixed to one piece and sliding along a slot in its neighbor. By the fifteenth century the knight "in full armor" was a familiar battlefield sight.109 Other innovations were in the air. In 1335 Guido da Vigevano, royal physician and astrologer at the French court, proposed what amounted to history's first tank, an armored wagon powered by a windmill mounted on top. In a more practical vein, Guido also suggested pontoon bridges and a.s.sault towers fabricated in small interchangeable sections that could be transported by pack animal and a.s.sembled in the field (his patron, Philip VI of France, was contemplating a Crusade). Guido's treatise has been called (by Bertrand Gille) a milestone between the notebook of Villard de Honnecourt and the great engineering sketchbooks of the fifteenth century.110 Crossbow confronts longbow at the Battle of Crecy, 1346. From the Chroniques of Froissart. [Bibliotheque de l'a.r.s.enal, Ms. 5187, f. 135v.]

Guido made no mention of firearms, which, however, had by this time made their un.o.btrusive entry on the stage. The first European mention of gunpowder occurs in 1268 in the writings of the English Franciscan friar Roger Bacon, in a pa.s.sage that Joseph Needham believes to be a description of Chinese firecrackers: We have an example of these things...in that children's toy which is made in many parts of the world: i.e., a device no bigger than one's thumb. From the violence of that salt called saltpeter together with sulfur and willow charcoal, combined into a powder, so horrible a sound is made by the bursting of a thing so small, no more than a bit of parchment containing it, that we find the ear a.s.saulted by a noise exceeding the roar of strong thunder, and a flash brighter than the most brilliant lightning. Especially if one is taken unawares, this terrible flash is very alarming. If an instrument of large size were used, no one could withstand the noise and blinding light, and if the instrument were made of solid material, the violence of the explosion would be much greater.111 How did Roger Bacon learn about Chinese fireworks? A possible explanation lies in the eastward journey of William of Rubruck a few years earlier. One of a number of European missionaries to visit China in the mid-thirteenth century, William was a fellow Franciscan and personal acquaintance of Roger. Needham speculates that William described Chinese firecrackers to his friend, or even brought some back with him as a curiosity.112 The employment of volatile mixtures in war had been familiar to both Europeans and Arabs ever since Greek fire was first used in the seventh century. By the same token, so was their discharge from a metal tube. But the use of such a mixture as a missile propellant was something new. Suddenly in the fourteenth century, niter, the sodium or pota.s.sium salt of nitric acid, also known as saltpeter, became the object of systematic collection from European barns, stables, and pigsties, to be mixed with sulfur and charcoal and ignited in metal tubes to propel missiles.

How this development came about remains a tantalizing mystery. Needham proposes three separate channels of communication from China: First, knowledge of gunpowder chemistry via missionaries like William of Rubruck or other European travelers. Second, knowledge arriving via the Arabs (a Spanish Muslim scientist referred to saltpeter as "Chinese snow") of bombs, rockets, and a weapon called the fire-lance, a bamboo, wood, or metal tube that spouted a mixture of pellets, pottery shards, and toxic chemicals in a stream that lasted some minutes. Third, by about 1300, knowledge of metal-barreled guns, possibly conveyed overland through Russia. That the Chinese were making gun barrels as early as 1300 is known from archaeological finds.113 Franciscan friar Roger Bacon. [Bodleian Library, Ms. Bodl. 211, p. 5.]

Little that is conclusive can be adduced from the evidence. Except for the pa.s.sage in Roger Bacon, no trace appears in either European or Islamic records of the kind of fumbling experimental steps by which China progressed to gunpowder weapons. Instead, a Florentine doc.u.ment of 1326 describes the city authorities' acquisition of metal cannon and iron shot in language indicating that the items were by then commonplace.114 In light of the Florentine doc.u.ment, Carlo Cipolla believes the "invention" of cannon to go back to the late thirteenth century. In light of the Florentine doc.u.ment, Carlo Cipolla believes the "invention" of cannon to go back to the late thirteenth century.115 The earliest doc.u.mented use of cannon in Europe was by two German knights at the siege of Cividale in northern Italy in 1331. Edward III brought at least twenty guns and large quant.i.ties of sulfur and saltpeter to the siege of Calais in 1346. The earliest doc.u.mented use of cannon in Europe was by two German knights at the siege of Cividale in northern Italy in 1331. Edward III brought at least twenty guns and large quant.i.ties of sulfur and saltpeter to the siege of Calais in 1346.116 Noteworthy is the fact that whatever the history of diffusion from China, Europeans had at this point not only overtaken the Chinese in firearms but surpa.s.sed them, since guns large enough to call cannon had not yet been manufactured in China, where cannon first appeared in the anti-Mongol revolution of 13561368. Noteworthy is the fact that whatever the history of diffusion from China, Europeans had at this point not only overtaken the Chinese in firearms but surpa.s.sed them, since guns large enough to call cannon had not yet been manufactured in China, where cannon first appeared in the anti-Mongol revolution of 13561368.117 In short, the priority of the invention of firearms is incontestably Chinese, and a high degree of probability exists, that most or all of the necessary knowledge was received by Europe from China. Yet some independent European contribution was involved, and Europe displayed an enthusiasm for the new weaponry that contrasts with Chinese indifference. Writing in the 1350s, Petrarch noted, "These instruments were a few years ago very rare...but now they are become as common and familiar as any other kind of arms. So quick and ingenious are the minds of men in learning the most pernicious arts."118 Early European cannon were made of copper, bra.s.s, or bronze, but a technique was soon devised for using the cheaper iron produced by the blast furnace as a practical gun material: the smith welded a cylinder of iron rods around a clay core to form a barrel, which he strengthened by shrinking iron bands around it. The core was then dug out. Cannonb.a.l.l.s were first made of lead or iron, then of cheaper stone, which the stonecutters fas.h.i.+oned with the aid of a "patron" or template of wood, parchment, or paper. But when it became possible to cast cannonb.a.l.l.s of iron, stone lost its advantage in price. Iron b.a.l.l.s may also have provided a better fit to gun bores. By 1418 the city of Ghent was ordering 7,200 cast-iron cannonb.a.l.l.s.119 Gunpowder was mixed in the field by the cannoneers, who were usually the same smiths who fabricated the cannon. Opinion varied on the proportions of saltpeter, sulfur, and carbon (charcoal), but medieval saltpeter content generally ran close to the 75 percent used for modern black powder. Gunpowder was mixed in the field by the cannoneers, who were usually the same smiths who fabricated the cannon. Opinion varied on the proportions of saltpeter, sulfur, and carbon (charcoal), but medieval saltpeter content generally ran close to the 75 percent used for modern black powder.120 Premature explosions were common. Premature explosions were common.

The first European handguns, which appeared at the end of the fourteenth century, suffered from other deficiencies. The gunner heated a wire red-hot, then had to aim his weapon while inserting the hot wire into a touchhole on the top of the barrel. A two-man version was easier to use-one man balancing the gun on his shoulder like a World War II bazooka while his mate applied the wire-but accidents were frequent.

Cannon on s.h.i.+pboard, with gun ports, 1482. [Bibliotheque Nationale, Ms. fr. 38, f. 157v.]

At the point when the first half of the Hundred Years War was terminated by a truce (1396), the new weapon had yet to prove its value. Despite greater range and accuracy and a more rapid rate of fire, it only slowly displaced the trebuchet (which threw a heavier missile). Unlike a trebuchet, a cannon could not be a.s.sembled in the field, nor was hauling it long distances easy. Two wagons in line provided a form of articulation, but the contraption often overturned. Arrived in the field, the gun had to be set up on a frame or trestle for firing, generally with mediocre effect.121 At the battle of Aljubarrota in 1385, the Castilians employed sixteen "great bombards," but the Portuguese, who had no cannon at all, won the battle. At the battle of Aljubarrota in 1385, the Castilians employed sixteen "great bombards," but the Portuguese, who had no cannon at all, won the battle.122 Early employment of gunpowder weapons at sea brought equally unimpressive results and turned up some fresh problems. Galleys, with their low freeboard, proved poor platforms for artillery, and on the decks and castles of deeper-hulled vessels cannon created top heaviness and instability in foul weather. The solution, a gun deck with gun ports pierced in the hull, was not found until the following century, when it introduced a whole new mode of naval warfare.

"A Wonderful Clock"

In the advance of Europe to the forefront of world technology, the emergence of the mechanical weight-driven clock in the second quarter of the fourteenth century has been widely regarded as a decisive moment. Donald Hill calls it "one of the main foundations for the development of machine technology in subsequent centuries,"123 and D. S. L. Cardwell describes it as "perhaps the greatest single human invention since the wheel." and D. S. L. Cardwell describes it as "perhaps the greatest single human invention since the wheel."124 At one time it was believed that the Western mechanical clock came into being in response to the monasteries' need for better timekeeping devices to govern their system of canonical hours. But the clepsydra adequately satisfied monastic needs, and in the early evolution of the clock, timekeeping was actually a secondary consideration. In Europe, as previously in Asia, clockwork developed out of the demand for precision instruments to aid in tracking stars and planets. The demand came from the astrologers, whose science was by now an established part of medical practice. Two of the clock's ancestors were the astrolabe, in its improved Islamic form, and the equatorium, another Muslim instrument, used to calculate positions of the planets on the basis of Ptolemy's system. The earliest Western "clocks," such as a famous one built by Richard of Wallingford in about 1320, have been described as "powered astronomical models," "artificial universes," and "pre-clocks."125 Weights as driving mechanisms had long been known, and gearing was by now thoroughly familiar to Europe's metal craftsmen. What was necessary to translate the gravitational pull into controlled motion was a means of governing the descent of the weight, whose natural tendency was to fall at an accelerating pace.126 The complex escapement of Su Sung, designed for a water-driven wheel, was never known in Europe. Villard de Honnecourt's notebook contains a sketch in which the statue of an angel is made to point continuously toward the sun by a wheel whose spokes strike a taut rope stretched by two weights: an escapement, but one so crude (and crudely represented) that it has only slowly been recognized as such and probably had no influence on the invention of the true clockwork escapement. The complex escapement of Su Sung, designed for a water-driven wheel, was never known in Europe. Villard de Honnecourt's notebook contains a sketch in which the statue of an angel is made to point continuously toward the sun by a wheel whose spokes strike a taut rope stretched by two weights: an escapement, but one so crude (and crudely represented) that it has only slowly been recognized as such and probably had no influence on the invention of the true clockwork escapement.127 The fact that Latin and the western European languages had no special terms to distinguish mechanical from water clocks has helped to obscure the story for modern historians. Abbott Payson Usher collected twenty references to clocks dating from between 1284 and 1335, all of which upon investigation turned out to be water clocks.128 Both Dante's Both Dante's Inferno Inferno (13081321) and the late-thirteenth-century (13081321) and the late-thirteenth-century Roman de la rose Roman de la rose contain literary references over which debate remains inconclusive. The origin of the European escapement is almost surely lost forever, but consensus today places it in the second half of the thirteenth century, contain literary references over which debate remains inconclusive. The origin of the European escapement is almost surely lost forever, but consensus today places it in the second half of the thirteenth century,129 and its emergence in the historical record signals its provenance as northern Italy. Joseph Needham believes in the possibility of stimulus diffusion of the idea of an escapement in the form of travelers' tales from China, but this hypothesis seems farfetched. As Carlo Cipolla says, "The Chinese escapement...had nothing in common with the European verge-and-foliot device." and its emergence in the historical record signals its provenance as northern Italy. Joseph Needham believes in the possibility of stimulus diffusion of the idea of an escapement in the form of travelers' tales from China, but this hypothesis seems farfetched. As Carlo Cipolla says, "The Chinese escapement...had nothing in common with the European verge-and-foliot device."130 What is certain is that the verge-and-foliot (or crown wheel and foliot) escapement is one of the most elegant solutions ever devised to a problem in mechanical engineering. What is certain is that the verge-and-foliot (or crown wheel and foliot) escapement is one of the most elegant solutions ever devised to a problem in mechanical engineering.

Verge-and-foliot escapement.

The essential parts of a verge-and-foliot escapement were the crown wheel, with triangular teeth set perpendicularly around its edge (like the points on a crown); the verge or rod, standing close to it, with two projections (pallets) perpendicular to each other, so placed as to engage with the crown wheel at its top and bottom; and the foliot, a crossbar balanced at the top of the verge, with weights at each end. As the weight-driven crown wheel turned, one of its teeth caught the upper pallet of the verge, which held it momentarily and then released it, giving a swing to the foliot with its weights. This caused the other pallet to engage the wheel, swinging the foliot in the opposite direction. Thus the wheel's motion was alternately arrested by the two pallets of the verge, and as the foliot swung back and forth, the wheel turned a click at a time. To regulate the clock, the speed of the mechanism could be increased or decreased by moving the weights on the arms of the foliot. One of the insights of the unknown inventor was the fact that the top and bottom of a revolving wheel are moving in opposite directions.131 The first mechanical clocks were huge iron-framed mechanisms, fabricated by blacksmiths and installed in towers; St. Eustorgio in Milan had one as early as 1309. They had no face or hands and did not strike the hours, but merely sounded an alarm which alerted the ringer to pull the bell rope. In 1335 the first clock that struck automatically, to the astonished admiration of the citizens, was also erected in Milan, in the tower of the Visconti palace chapel. "There is a wonderful clock with a very large clapper," wrote a contemporary, "which strikes a bell twenty-four times according to the twenty-four hours of the day and night, and thus at the first hour of the night gives one sound, at the second two strokes...and so distinguishes one hour from another which is of the greatest use to men of every degree."132 L'Horloge de Sapience (The Clock of Wisdom), c. 1450. At left, a clock with an hour hand and twenty-four-hour face; an astrolabe hangs below it. The table on the right bears a clock that may be the first evidence of a spring-driven timekeeper. [Bibliotheque Royale, Brussels, Ms. IV, III, f. 13v.] (The Clock of Wisdom), c. 1450. At left, a clock with an hour hand and twenty-four-hour face; an astrolabe hangs below it. The table on the right bears a clock that may be the first evidence of a spring-driven timekeeper. [Bibliotheque Royale, Brussels, Ms. IV, III, f. 13v.]

The earliest known makers of real (timekeeping) mechanical clocks are Jacopo di Dondi and his son Giovanni. In 1344 Jacopo created a clock for the entrance tower of the Carrara palace at Padua, which besides automatically indicating "the intervals of four-and-twenty hours by day and night" showed the phases of the moon and other astronomical features. A clock built by Giovanni di Dondi for the castle of Pavia, installed in 1364, has been described as "a true mechanical clock," equipped with weight drive, verge-and-foliot escapement, seven dials with gear wheels and linkages to show astronomical motions, a fully automated calendar showing the holy days, and, almost as an afterthought, a small dial for telling time.133 Once the verge-and-foliot escapement became known, blacksmiths in cities all over Europe began turning out clocks. By 1370 at least thirty had been installed, all with timekeeping an inconspicuous and only moderately successful function.134 The astronomical garnishment, on the other hand, quickly came to serve an aesthetic as well as a scientific function. The city clock became a source of civic pride, "a marvel, an ornament, a plaything...a part of the munic.i.p.al adornment, more a prestige item than a utilitarian device" (Jacques Le Goff). The astronomical garnishment, on the other hand, quickly came to serve an aesthetic as well as a scientific function. The city clock became a source of civic pride, "a marvel, an ornament, a plaything...a part of the munic.i.p.al adornment, more a prestige item than a utilitarian device" (Jacques Le Goff).135 The enormous clock built at Strasbourg in 1354 included a moving calendar; an astrolabe whose pointers indicated the movements of the sun, moon, and planets; a statue of the Virgin before whom every noontime the Magi bowed while the carillon played a tune; and, atop the whole, a large c.o.c.k that opened its beak, crowed, and flapped its wings. The enormous clock built at Strasbourg in 1354 included a moving calendar; an astrolabe whose pointers indicated the movements of the sun, moon, and planets; a statue of the Virgin before whom every noontime the Magi bowed while the carillon played a tune; and, atop the whole, a large c.o.c.k that opened its beak, crowed, and flapped its wings.136 The attention given by the clockmaking smiths to such ornate details may have detracted from that given to precision instrumentation. Most medieval clocks gained or lost many minutes in twenty-four hours. At first n.o.body cared very much. Contemporary requirements for accuracy were liberal. Though astronomers had by now subdivided the day's hours into sixty-second minutes, a system borrowed from ancient Babylon, medieval people had long been accustomed to variable winter and summer hours, to fit the daylight available for work.

It was the new clocks, with their noisy officiousness, that gradually imposed the system of equal hours, causing people to begin timing activities that no one had thought of timing before. In the cloth-making towns of Flanders, the clocks struck the working hours of the textile workers. Forthwith, "the communal clock [became] an instrument of economic, social, and political domination wielded by the merchants who ran the commune" (Le Goff).137 In Paris in 1370, Charles V ordered all the bells of the city to keep time with the clock in the Palais-Royal as it rang the hours and quarter hours, regimenting the city into a uniform time frame. Uniform, but not notably reliable, as a Parisian verse observed: In Paris in 1370, Charles V ordered all the bells of the city to keep time with the clock in the Palais-Royal as it rang the hours and quarter hours, regimenting the city into a uniform time frame. Uniform, but not notably reliable, as a Parisian verse observed: L'horloge du palaisElle vas comme il lui plait.138 (The palace clock/It goes as it pleases.) The uniformity was local rather than national. Each city set its own zero hour-sometimes noon, sometimes midnight, but more often sunrise or sunset, creating a confusion that continued to baffle travelers into the fifteenth and sixteenth centuries.

The first household clocks appeared shortly before 1400. In contrast to the big tower clocks made by blacksmiths, the smaller versions had faces, hour hands, and later minute hands, and were the work of goldsmiths and silversmiths.139 One of the most significant things about medieval clockwork is simply that these were the very first machines made entirely of metal; all preceding machinery had been mainly wooden. The metal smiths' tradition of precision work, here established, lasted all the way into the eighteenth century, when it gave them a key role in fabricating and operating the textile machinery of the Industrial Revolution.

Meanwhile, the mechanical clock, invented as an almost incidental component of a mechanism designed to serve the needs of the pseudoscience of astrology, rapidly acquired its own significance. Once people could time their activities, they subordinated them to time, working and living by the hour, in a new rhythm that continues to this day.

Wheels of Travel, Wheels of Commerce As the Commercial Revolution increased the strain on road surfaces, it also heightened the influence of the merchants who paid the tolls and taxes. For the first time serious effort went into road maintenance. Old roads were repaired and new ones built, employing the established technique of cobbles or broken stone on a foundation of loose sand. Not as strong and rigid as the Roman road, the medieval road was easier to maintain and on the whole better suited to vehicular traffic. In some locations, mainly within cities, mortared paving blocks were used.140 All over northwest Europe the road paver became a familiar sight, in France and Flanders sitting on a four-legged stool and moving forward as he worked, in Germany sitting on a one-legged stool and moving backward. All over northwest Europe the road paver became a familiar sight, in France and Flanders sitting on a four-legged stool and moving forward as he worked, in Germany sitting on a one-legged stool and moving backward.141 Where grades were excessive for wagons, as so often in Switzerland, standby draft animals were stationed to be added to teams as needed. In 1237 a new road and "daring bridges" (Robert Lopez) opened the St. Gothard Pa.s.s to pack animals. One narrow stone arch over the rapids of the Reuss was called the Pont Ec.u.mant (Foaming Bridge) because of the spray that perpetually drenched drivers and animals. In the following century the Swiss opened the first Alpine road capable of accommodating wheeled traffic, over Monte Settimo.142 Elsewhere, the bridge-building boom of the eleventh and twelfth centuries peaked in the thirteenth.143 In the Ile-de-France, eight new bridges were built in the eleventh century, seventeen in the twelfth, and thirty-four in the thirteenth. In the Ile-de-France, eight new bridges were built in the eleventh century, seventeen in the twelfth, and thirty-four in the thirteenth.144 As commerce furnished an ever larger element in the traffic, the towns increasingly a.s.sumed responsibility for bridge construction and maintenance. The old Roman concept of bridges as public works revived, together with the idea of financing them by taxation. St. Benezet's Pont d'Avignon pa.s.sed from the aegis of the Bridge Brothers to that of the communal government. The tradition of private support did not die out, however. In the fifteenth century, donations were still being received, such as that following a disastrous flood of the Loire from "a person who had great love and affection for the bridge [at Orleans] and its rebuilding." As commerce furnished an ever larger element in the traffic, the towns increasingly a.s.sumed responsibility for bridge construction and maintenance. The old Roman concept of bridges as public works revived, together with the idea of financing them by taxation. St. Benezet's Pont d'Avignon pa.s.sed from the aegis of the Bridge Brothers to that of the communal government. The tradition of private support did not die out, however. In the fifteenth century, donations were still being received, such as that following a disastrous flood of the Loire from "a person who had great love and affection for the bridge [at Orleans] and its rebuilding."145 Some new construction techniques appeared. One of Villard de Honnecourt's sketches shows a machine for sawing off the tops of bridge piles.146 The Roman cofferdam came back into use; saplings were driven into the riverbed to form an enclosure which was pumped out, and the piles driven for the pier foundation, with a core of rubble or stamped-down clay and masonry blocks laid on top. By this rough-and-ready method, several bridges of record-breaking length were built: the 54-meter (175-foot) single arch over the Allier at Vieille-Brioude, in southern France, built in the 1340s (and lasting until 1822) The Roman cofferdam came back into use; saplings were driven into the riverbed to form an enclosure which was pumped out, and the piles driven for the pier foundation, with a core of rubble or stamped-down clay and masonry blocks laid on top. By this rough-and-ready method, several bridges of record-breaking length were built: the 54-meter (175-foot) single arch over the Allier at Vieille-Brioude, in southern France, built in the 1340s (and lasting until 1822)147 and in the 1370s the even longer arch over the Adda at Trezzo in northern Italy, at 72 meters (236 feet) the world's longest single-arch span until the eighteenth century. The Karlsbrucke at Prague, begun by the Emperor Karl IV to bridge the broad Moldau, took forever to finish, owing to the Hussite wars and other interruptions, but when finally completed in 1503 it was, at nearly 600 meters (1,970 feet), the world's longest stone-arch bridge. and in the 1370s the even longer arch over the Adda at Trezzo in northern Italy, at 72 meters (236 feet) the world's longest single-arch span until the eighteenth century. The Karlsbrucke at Prague, begun by the Emperor Karl IV to bridge the broad Moldau, took forever to finish, owing to the Hussite wars and other interruptions, but when finally completed in 1503 it was, at nearly 600 meters (1,970 feet), the world's longest stone-arch bridge.148 The caption reads: "By this means, one can cut off the tops of piles under water so as to set a pier on them." [From The Notebook of Villard de Honnecourt, The Notebook of Villard de Honnecourt, ed. by Theodore Bowie, Indiana University Press.] ed. by Theodore Bowie, Indiana University Press.]

Regular contracts were now awarded to masons and to the carpenters who built the falsework to support the arches during construction. For some bridges, especially those near cities, periodic inspections were carried out by teams of masons, carpenters, and communal officials. Innovations in design were few, though a fine model of the segmental arch bridge appeared in Florence in 1345, in what came to be known as the Ponte Vecchio (Old Bridge). Whether Taddeo Gaddi, its architect, was acquainted with the Pont-St.-Esprit in France is unknown; his segmental arch was a novelty in Italy. The reduction in scour effected by the narrower piers of the segmental form helped the bridge, crowded with shops, houses, and tourists, to survive Arno floods to the present day.

Far more numerous than the stone bridges were those built of timber, but few traces of these remain. Two survivors are the famous Kapellbrucke and Spreuerbrucke of Lucerne, Switzerland, known chiefly for their mural galleries but of technical importance for their partial truss construction. The truss design, based on the structural strength of the triangle, had a long history as a roof support but was only tardily exploited as a bridge form. The function of the picturesque roof and siding was to protect the structural members of the truss from alternations of wet and dry weather. The inclusion of a kind of truss in Villard de Honnecourt's notebook, and of several variations in Andrea Palladio's Treatise on Architecture Treatise on Architecture of 1570, suggests that the form was widely used for short crossings. Villard also depicts a cantilever, a balanced structure usually employed in pairs to form a bridge. Long produced in stone in China and India, the cantilever was not adopted in Europe until the nineteenth century. of 1570, suggests that the form was widely used for short crossings. Villard also depicts a cantilever, a balanced structure usually employed in pairs to form a bridge. Long produced in stone in China and India, the cantilever was not adopted in Europe until the nineteenth century.149

While the total number of vehicles of all types multiplied on the roads, s.h.i.+fts took place in the proportions of the categories. Four-wheeled wagons, long outnumbered by two-wheeled carts, became much more common, while at the upper end of the social scale the first carriages offering a degree of comfort were introduced. Chariots branlants Chariots branlants, or "rocking carriages," were used by great n.o.bles and ladies from at least the 1370s. Until then, in the words of Marjorie Boyer, "the cha.s.sis of a lady's personal char char was essentially no different from the chariot in which her baggage was transported," the carriage body resting directly on the axles and transmitting every b.u.mp in the road to its occupants. The "rocking carriage," employing chains hung from posts run transversely under the body, somewhat ameliorated the jolting. An ill.u.s.tration from a Zurich ma.n.u.script of the mid-fourteenth century shows what seems to be the longitudinal suspension of a carriage body from leather straps, but such carriages did not arrive in numbers in western Europe until the following century. Their origin was Hungary, where the town of Kocs (hence "coach," was essentially no different from the chariot in which her baggage was transported," the carriage body resting directly on the axles and transmitting every b.u.mp in the road to its occupants. The "rocking carriage," employing chains hung from posts run transversely under the body, somewhat ameliorated the jolting. An ill.u.s.tration from a Zurich ma.n.u.script of the mid-fourteenth century shows what seems to be the longitudinal suspension of a carriage body from leather straps, but such carriages did not arrive in numbers in western Europe until the following century. Their origin was Hungary, where the town of Kocs (hence "coach," coche, Kutsche coche, Kutsche) became famous for its lightweight, one-horse, leather-suspended pa.s.senger vehicles.150 Eventually wagons were also improved by suspension, although the change came only slowly, and to the end of the Middle Ages merchandise was damaged and the wagons themselves were jarred to pieces by the unrelieved shocks of ruts and potholes. Protection of merchandise from the weather, however, was effected by the longa caretta longa caretta, twelfth-century ancestor of the Conestoga wagon.151 The advance to four-wheeled wagons was a.s.sisted by the movable forecarriage, which appeared before the end of the fourteenth century, greatly reducing the turning radius, but once more general adoption was slow.152 Wheels were provided with iron tires in the form of a number of small plates, clumsily nailed on. The technique of shrinking heated bands onto wheels was not invented until the sixteenth century. Wheels were provided with iron tires in the form of a number of small plates, clumsily nailed on. The technique of shrinking heated bands onto wheels was not invented until the sixteenth century.

Despite shortcomings, wagons were stronger and more durable, and animal harness more efficient than in previous centuries. For carriages, the breast harness was favored, in the shape of a long leather strap pa.s.sing completely around the animal horizontally, forming a strap across the chest to pull against and a strap across the rump to hold back the weight when descending a hill.153 By the high Middle Ages, land transport was significantly cheaper. Wagons could carry goods twenty-two to thirty-five kilometers (fourteen to twenty-two miles) a day in level country, adding a transportation cost per eighty kilometers (fifty miles) traveled that for wool amounted to only about 1.5 percent, for grain about 15 percent.154 Pack animals, which still carried most of the freight, achieved even better speed. Pack animals, which still carried most of the freight, achieved even better speed.155 In the summer of 1375, William de Percelay carried sacks of silver pennies representing the arrears of the ransom of David, king of Scotland, from York to London at an average speed of fifty-five kilometers (thirty-eight miles) a day. Riding home empty-handed, William made better than sixty kilometers (forty-five miles) a day. In the summer of 1375, William de Percelay carried sacks of silver pennies representing the arrears of the ransom of David, king of Scotland, from York to London at an average speed of fifty-five kilometers (thirty-eight miles) a day. Riding home empty-handed, William made better than sixty kilometers (forty-five miles) a day.156 William was traveling alone; n.o.blemen, kings, and prelates, who might be expected to travel fastest, were handicapped by their retinues, for whom accommodations had to be found, and rarely did better than about thirty miles a day.157 More important for the Commercial Revolution was the improved speed of messengers carrying commodity and price information from the Champagne Fairs and other markets to home offices in Italy and, in the opposite direction, instructions to local agents. More important for the Commercial Revolution was the improved speed of messengers carrying commodity and price information from the Champagne Fairs and other markets to home offices in Italy and, in the opposite direction, instructions to local agents.158 The slowest component of traffic was droves of animals. In May 1323 John the Barber set out from Long Sutton, near King's Lynn, with 19 cows and a bull, 313 ewes, 192 hogs, 172 lambs, and a bellwether, on the 130-mile journey to Tadcaster, in Yorks.h.i.+re, evidently to stock the royal manors there. He had to hire a shepherd and eight boys to a.s.sist him, as well as twelve local boys "to chase the said animals through the town of Boston," a cavalcade that must have disturbed the townspeople no matter how well controlled. John covered twelve miles in the first two days, and a second twelve in one day, evidently more level going; the next eighteen miles took two days, and at the end of a week he had traveled fifty-six miles. At this point he picked up several hundred additional animals plus more boys and another shepherd. Six more days over a more direct road often used by drovers took him the remaining seventy-four miles, making his average for the whole arduous trip ten miles a day.159

In inland water transportation, conflicts between waterpower and navigation rights multiplied with the increasing traffic. One technological solution was the navigation weir, a small dam only partially blocking the waterway while maintaining stream depth. Its drawback, the obstacle to upstream traffic created by the strong constricted current, was dealt with by installing an animal-powered windla.s.s to haul vessels past the dam. The Low Countries, where almost 85 percent of traffic moved on inland waterways, pioneered ca.n.a.l locks at Damme and elsewhere in the late fourteenth century, but early lock gates-double doors or vertical portcullis-had problems that awaited solution in the following century.160 Navigation: The Compa.s.s Matures While better roads, bridges, and vehicles gradually speeded land transportation, Mediterranean s.h.i.+pping underwent a revolution in both technology and function beginning in the thirteenth century, doubling the number of voyages per year to Egypt and the Levant, and a.s.suming the main burden of the trade between Italy and Flanders, heretofore carried overland via the Champagne Fairs.

Two important new types of s.h.i.+p contributed. The "Great Galley" introduced by the Venetian a.r.s.enal was not a galley at all but a sailing s.h.i.+p that used oars for entering and leaving port.161 Its two, later three, masts were lateen rigged, with the large mainsail supplying most of the wind power. Its hold accommodated 150 tons, silks and spices on the northern trip, wool cloth or raw wool on the return. Its two, later three, masts were lateen rigged, with the large mainsail supplying most of the wind power. Its hold accommodated 150 tons, silks and spices on the northern trip, wool cloth or raw wool on the return.162 An even more useful north-to-south carrier was a new model of the northern cog, introduced into the Mediterranean about 1300.163 Earlier square-sailed northern s.h.i.+ps had encountered a peculiar difficulty in the Mediterranean. The westerly wind that prevailed in the Strait of Gibraltar carried them in easily enough but virtually blocked their pa.s.sage out again. Better rigging overcame that problem, and in the fourteenth century the sailing ability of the cog was given a basic improvement with the addition of a second (mizzen) mast equipped with a lateen sail. Earlier square-sailed northern s.h.i.+ps had encountered a peculiar difficulty in the Mediterranean. The westerly wind that prevailed in the Strait of Gibraltar carried them in easily enough but virtually blocked their pa.s.sage out again. Better rigging overcame that problem, and in the fourteenth century the sailing ability of the cog was given a basic improvement with the addition of a second (mizzen) mast equipped with a lateen sail.164 The new cog found special favor with the Genoese, who used it to carry alum, a color fixative, from the islands of Phocaea and Chios in the Aegean Sea direct to Flanders and England. While adhering to traditional carvel-skeletal construction, Genoese s.h.i.+pyards progressively increased the size of their hulls, by 1400 reaching cargo capacities of 600 tons, three times the size of the Hanseatic bulk carriers. The new cog found special favor with the Genoese, who used it to carry alum, a color fixative, from the islands of Phocaea and Chios in the Aegean Sea direct to Flanders and England. While adhering to traditional carvel-skeletal construction, Genoese s.h.i.+pyards progressively increased the size of their hulls, by 1400 reaching cargo capacities of 600 tons, three times the size of the Hanseatic bulk carriers.165 The "castles," fore- and stern-, that the northern cog had added in the eleventh century were gradually absorbed in Mediterranean s.h.i.+pbuilding into the lines of the hull and proved as effective against the pirates of the Mediterranean as against those of the Baltic. Used as a shelter for crew and for spare rigging, the forecastle became a permanent feature of sailing s.h.i.+ps.

The old-fas.h.i.+oned galley and lateen-rigged sailing s.h.i.+p were not completely eclipsed, despite their higher costs owing to larger crews and smaller cargo capacity. The lateen sailer was especially valuable for cabotage (coastal tramping), where maneuverability was at a premium, while the galley continued to be favored by pilgrims, for whom, in the post-Crusading world, Venice was the leading port of embarkation. The galleys' operating procedure of putting into port every night suited this cla.s.s of medieval travelers, who in addition to improving their spiritual condition liked to make the most of the trip, dining and sleeping onsh.o.r.e and seeing the sights. On the round s.h.i.+ps' express voyage to Syria, pa.s.sengers had to carry food for the whole trip and glimpsed famous cities only from afar. Fares were lower, but conditions were steerage as opposed to first cla.s.s.166 The maturing of the compa.s.s as a navigation instrument took place in the Mediterranean, partly because this narrow but deep sea did not permit navigation by sounding and partly because its seafarers were the most sophisticated navigators and thus were able to supply important complementary devices. The first of these was the compa.s.s card, contributed by the sailors of Amalfi and based on the ancient Rosa Ventorum Rosa Ventorum or "Rose of the Winds." A circular card furnished with the thirty-two points of the compa.s.s and positioned directly beneath the free-swinging magnetized needle fixed on a dry pivot, it allowed the helmsman to read the s.h.i.+p's course-in points, not degrees, since the thirty-two-point scale was incompatible with the 360 degrees of the astronomer's circle. or "Rose of the Winds." A circular card furnished with the thirty-two points of the compa.s.s and positioned directly beneath the free-swinging magnetized needle fixed on a dry pivot, it allowed the helmsman to read the s.h.i.+p's course-in points, not degrees, since the thirty-two-point scale was incompatible with the 360 degrees of the astronomer's circle.

Model of fourteenth-century Mediterranean sailing s.h.i.+p has new-style castles but old-fas.h.i.+oned steering oar. [Science Museum, London.]

The second auxiliary device was the "portolan" (port-finding) chart, the world's first navigational chart. Experienced Italian sailors felt their way on repeat voyages by sailing from one island or headland to the next, setting their course by compa.s.s and estimating the distance traveled on each bearing. A natural advance was to compile sailing directions that described coastlines and specified bearings and distances between points so that skippers unfamiliar with a given s.h.i.+pping route could benefit. In the late thirteenth or early fourteenth century, someone had an insight: such information could be represented geometrically with two large circles superimposed on the whole Mediterranean, one with a center just west of Sardinia, the other with a center on the Ionian coast north of Rhodes.167 Besides compa.s.s and charts, Mediterranean s.h.i.+ps took to carrying hourgla.s.ses to aid in calculating s.h.i.+p speed and distance traveled. The astrolabe also made its appearance on board s.h.i.+p, again in the vanguard Mediterranean, where its value-determining lat.i.tude-was marginal.

Whether the new s.h.i.+p types or the new navigating techniques had more to do with the revolution in Mediterranean s.h.i.+pping operations that followed is a matter of scholarly controversy.168 Both contributed to a startling change: after millennia of sailing back and forth once a year, Italy to Egypt or Asia Minor, Italian fleets took to making two such voyages. Venetian s.h.i.+ps departed in February and returned in May, left again about the first of August and returned before Christmas. The Genoese also ceased wintering in the East and came home in time to launch a second voyage. After 1280 Pisan records too show s.h.i.+ps sailing in all seasons, including the dead of winter. Both contributed to a startling change: after millennia of sailing back and forth once a year, Italy to Egypt or Asia Minor, Italian fleets took to making two such voyages. Venetian s.h.i.+ps departed in February and returned in May, left again about the first of August and returned before Christmas. The Genoese also ceased wintering in the East and came home in time to launch a second voyage. After 1280 Pisan records too show s.h.i.+ps sailing in all seasons, including the dead of winter.169 With the difficulties of winter navigation overcome, its advantage became apparent: better prevailing winds. s.h.i.+ps departing from Egypt in the months from May to October faced almost steady northerly and northwesterly winds, forcing them to detour around Cyprus or Rhodes, whereas in late fall the wind s.h.i.+fted to easterly, favoring the return to Italy. The new large s.h.i.+ps also encouraged the Italian venture into the North Sea. The first recorded commercial penetration there was made by Genoese galleys in 127778; sailing s.h.i.+ps quickly followed, and by 1314 Venetian voyages to Flanders were safe and regular.170 In northern waters, the value of the compa.s.s was reduced by the shallowness of the Baltic and North Seas, which permitted navigation by lead and line. But for voyages into the broad and deep Atlantic, it was invaluable, and such voyages were becoming more common for adventurous fishermen. About 1330 William Beukelszoon pioneered the practice of gutting herring at sea, improving preservation and making possible much longer fis.h.i.+ng expeditions.171 By the mid-fourteenth century, the new navigation and the new s.h.i.+p rigging were in general use in the northern and southern seas and in the Atlantic. In 1354 Pedro IV of Aragon ordered all his s.h.i.+ps to carry charts. By this time too, trigonometry, developed in the universities, was being applied to navigation.172 The possibility now arose of global voyages, the unlimited exploration of all the fabled seven seas. The possibility now arose of global voyages, the unlimited exploration of all the fabled seven seas.

"The Investigation of Causes": The Scientific Att.i.tude Around the year 1180, a Pisan merchant was appointed to the post of customs official, or consul, of the Pisan community in Bougia, Muslim North Africa. After settling there, he sent for his son Leonardo Fibonacci,* who was still "in his boyhood" ( who was still "in his boyhood" (pueritas), to complete his education "with a view to future usefulness," a commentary on the new att.i.tude toward Islam developing among the European business cla.s.s. In his new home, Leonardo made the discovery of Hindu-Arabic numerals.

Adelard of Bath's translation of al-Khwarizmi had expounded the Hindu notation but only to a very limited circle even among the mathematically literate. Leonardo perceived its enormous potential value and in 1202 undertook its wider diffusion by writing what proved to be a seminal book in the history of mathematics and science, the Liber abaci Liber abaci (Book of the abacus). The book began: "The nine Indian figures are 9 8 7 6 5 4 3 2 1. With these nine figures and the sign 0, any number may be written, as is demonstrated below." (Book of the abacus). The book began: "The nine Indian figures are 9 8 7 6 5 4 3 2 1. With these nine figures and the sign 0, any number may be written, as is demonstrated below."173 Many of the problems presented by Leonardo in the Liber abaci Liber abaci dealt with practical business matters, such as calculation of interest, margins of profit, percentages of alloys in coinage, and prices; others were recreational. Methods of solution were borrowed from the Hindus and the Arabs, with some refinements of Leonardo's own. His main contribution to mathematics, beyond the introduction of the Hindu numerals, was in number theory. He is recognized today chiefly as the originator of the "Fibonacci sequence," the first recursive number sequence (sequence in which the relation between two or more successive terms can be expressed by a formula) known in Europe. dealt with practical business matters, such as calculation of interest, margins of profit, percentages of alloys in coinage, and prices; others were recreational. Methods of solution were borrowed from the Hindus and the Arabs, with some refinements of Leonardo's own. His main contribution to mathematics, beyond the introduction of the Hindu numerals, was in number theory. He is recognized today chiefly as the originator of the "Fibonacci sequence," the first recursive number sequence (sequence in which the relation between two or more successive terms can be expressed by a formula) known in Europe.174 Leonardo's greatest achievement in number theory, however, was in Diophantine algebra, a discipline named for a fourth-century Alexandrian mathematician. Leonardo's algebra, like that of the Hindus, was rhetorical-expressed in words rather than symbols, with res res (thing) for an unknown, (thing) for an unknown, quadratus numerus quadratus numerus (square number) for (square number) for x x2, and cubus numerus cubus numerus (cube number) for (cube number) for x x3. His problems, however, were accompanied by diagrams with letter labels representing the unknowns, usually a a (alpha), (alpha), b b (beta), and (beta), and g g (gamma), prefiguring the modern (gamma), prefiguring the modern x, y x, y, and z z. Signs to indicate operations did not appear until centuries after Leonardo's death-the plus and minus signs in the fifteenth century, equals in the sixteenth, division in the seventeenth.175 For a time businessmen were wary of the new numerals, partly out of general conservatism, partly because it was felt that they could be more easily altered by the unscrupulous, and finally because they necessitated memorizing tables of multiplication and division. But by the late fourteenth century, Hindu numerals were displacing both Roman numerals and the calculating board in European commerce. They also found their way into the literature of everyday life, although Roman numerals lingered in many places. In advanced Italy, the Datini correspondence employs the Hindu numerals and only occasionally lapses into Roman, but in more backward England a century later the letters of the Paston family still use Roman, even in dates: "Wretyn...on the Frydaye next Seynt Symonds and Jude, anno E. iiii xix" (Written...on the Friday after St. Simon and Jude's Day in the 19th year of Edward IV).176 Eventually the Roman figures were relegated to secondary status, in uses such as outlines and cornerstone inscriptions. Eventually the Roman figures were relegated to secondary status, in uses such as outlines and cornerstone inscriptions.

Most significant was the impact of the Hindu notation on science and mathematics. Charles Singer calls it "a major factor in the rise of science" in the Western world.177 The beginnings of Western trigonometry trace to the imposition of the methods of Euclid by Richard of Wallingford (c. 12921335) of Merton College, Oxford, on the "Toledan Tables" of the Arabic mathematician al-Zarqali. The beginnings of Western trigonometry trace to the imposition of the methods of Euclid by Richard of Wallingford (c. 12921335) of Merton College, Oxford, on the "Toledan Tables" of the Arabic mathematician al-Zarqali.178 Mathematics was essential to the pursuit of the study of optics, one of the favored sciences of the universities, whose clerical intellectuals were inspired or justified by Biblical citations. "In G.o.d's Scriptures," wrote Roger Bacon, "nothing is so much enlarged upon as those things that pertain to the eye and vision." Mathematics was essential to the pursuit of the study of optics, one of the favored sciences of the universities, whose clerical intellectuals were inspired or justified by Biblical citations. "In G.o.d's Scriptures," wrote Roger Bacon, "nothing is so much enlarged upon as those things that pertain to the eye and vision."179 The Oxford master most noted for his interest in "the metaphysics of light" was Roger Bacon's mentor and one of the outstanding intellectuals of the thirteenth century, Robert Grosseteste (c. 11751253), in his later years bishop of Lincoln. Grosseteste perceived light as the cause of motion and the principle of intelligibility in the universe and strove to answer questions such as how the sun produces heat and how the moon influences the tides. The Oxford master most noted for his interest in "the metaphysics of light" was Roger Bacon's mentor and one of the outstanding intellectuals of the thirteenth century, Robert Grosseteste (c. 11751253), in his later years bishop of Lincoln. Grosseteste perceived light as the cause of motion and the principle of intelligibility in the universe and strove to answer questions such as how the sun produces heat and how the moon influences the tides.180 On the practical level, the invention of eyegla.s.ses occurred in Italy sometime before 1292, facilitated by the gla.s.smakers' mastery of the art of making clear gla.s.s. The first gla.s.ses had convex lenses, improving vision for the farsighted. Concave lenses, for the nearsighted, did not arrive until the sixteenth century. On the practical level, the invention of eyegla.s.ses occurred in Italy sometime before 1292, facilitated by the gla.s.smakers' mastery of the art of making clear gla.s.s. The first gla.s.ses had convex lenses, improving vision for the farsighted. Concave lenses, for the nearsighted, did not arrive until the sixteenth century.

In the universities some of the new eyegla.s.ses were focused on rediscovered Aristotle, of whose works two thousand ma.n.u.script copies survive from the thirteenth and fourteenth centuries.181 The other Greek "authorities" were likewise copied and recopied. The attraction of Greek knowledge lay in both quant.i.ty and form. "Arranged in neat compartments, it was presented in elegant, rational, and sophisticated fas.h.i.+on, and it contained an enormous amount of factual information about the natural world as well as highly developed methods of investigating that world" (Richard Dales). The other Greek "authorities" were likewise copied and recopied. The attraction of Greek knowledge lay in both quant.i.ty and form. "Arranged in neat compartments, it was presented in elegant, rational, and sophisticated fas.h.i.+on, and it contained an enormous amount of factual information about the natural world as well as highly developed methods of investigating that world" (Richard Dales).182 Investigating the world was a project with immense appeal. Much as they loved Aristotle, the university scholars did not hesitate to criticize him on the basis of what they learned from their own experience. "Natural science," said Albertus Magnus (c. 12001280), one of the luminaries of the University of Paris, "is not simply receiving what one is told, but the investigation of causes of natural phenomena." Investigating the world was a project with immense appe